The commentaries are somewhat troubled with the meaning of these two passages. But before considering their concern, let us understand the simple meaning of the passages. Moshe warns the nation that they should not succumb to the temptation to adopt the idolatrous practices prevalent in the land of Canaan. Moshe warns the people that Hashem regards these practices as abominations. In order to emphasize this point, he notes that these idolaters even burned their own children in order to appease their gods.
However, Moshe adds one other observation. He points out that these nations will be destroyed. He tells the people that once they have seen that these nations have been destroyed, they should not be tempted to adopt the forms of worship that they employed. Moshe implies that the destruction of these nations is somehow relevant to the admonition against adopting their various modes of worship. It is this implication that troubled the commentaries. What exactly is the connection between the destruction of the nations of Canaan and the admonition against adopting their various forms of idolatrous worship?
Rashi suggests that the destruction of these nations proves the impotence of their supposed gods and the ineffectiveness of the various ways in which they were worshiped. In other words, Moshe points out to Bnai Yisrael that these nations worshiped false gods through ineffective forms of worship and they were destroyed. This should indicate to Bnai Yisrael that if they abandon Hashem and adopt the idolatry of the nations of Canaan, then they too will be destroyed.
However, Nachmanides rejects this interpretation. Nachmanides does not elaborate on his reasons for rejecting Rashi’s interpretation of this element of the passage. However, Rav Naftali Tzvi Berlin – Netziv – does discuss this issue. He explains that according to Rashi it would seem that Moshe admonishes the people to reject idolatry because it is not effective. Netziv explains that such an interpretation of the passage is problematic. We do not reject idolatry because it is ineffective. We reject it because it is false! It is inappropriate to imply that we should reject idolatry simply because it is not effective.
However, Nachmanides must explain Moshe’s message in referring to the destruction of the nations of Canaan. Nachmanides explanation of this reference is based on his interpretation of Moshe’s overall message. What is Moshe’s specific admonishment? If we carefully consider Moshe’s words, there is some ambiguity. He tells the nation they it should not adopt the practices of the idolaters of Canaan. However, was Moshe merely telling the people – once again – to not worship idols? Nachmanides suggests that Moshe’s message is not a repetition of the often stated injunction against idolatry. He suggests that Moshe is making a new point. We are not permitted to incorporate the various modes of worship employed by the idolaters into our worship of Hashem. In other words, we are prohibited against identifying worship services and rituals from other nations and incorporating these rituals into the service of Hashem.
Based on this interpretation, Nachmanides reinterprets Moshe’s reference to the destruction of the nations of Canaan. Moshe is concerned that the people may find some allure in these alien services. They may conclude that these services are really suitable modes of worship. However, they were used by the nations of Canaan in the worship of false gods. These nations perverted services that should have been used in the worship of Hashem and applied them to the worship of idols. This is one of the reasons they were destroyed. In other words, Moshe warned the people that they should not misinterpret Hashem’s reasons for destroying the nations of Canaan. They should not conclude that these nations were destroyed because they desecrated the honor of Hashem by employing modes of worship in the service of other gods that are only fit for Him. Instead, they must realize that the modes of worship employed by the idolaters are innately reprehensible. It is not appropriate to adopt these practices and incorporate them into our service of Hashem.
Nachmanides points out that his interpretation of Moshe’s opening remark is consistent with the remainder of his address on this issue. Next, Moshe observes that the nations of Canaan even sacrificed their own children to their false gods. Nachmanides explains that this observation is completely consistent with his interpretation of Moshe’s message. Moshe is proving that the rituals employed by the idolaters of Canaan are inherently abhorrent. Their very concept of appropriate worship is grossly misguided. The proof is that for the sake of worship, they sacrificed their own children.
In summary, Nachmanides makes three important points. First, he explains that idolatrous practices should not be incorporated into the service of Hashem. It would seem that Nachmanides would extend this injunction to practices and rituals from any other religion. They should not be adopted.
Second, these idolatrous practices are not inappropriate merely because they are associated with idolatry. They are innately objectionable. They reflect a perverted concept of worship. The depravity of the idolatrous concept of worship is indicated by the practice of child sacrifice.
Third, Nachmanides implies that the modes of worship established by the Torah are not arbitrary. They are meaningful and appropriate. They are selected by the Torah because they reflect a suitable attitude and outlook regarding service of Hashem.
It is possible to understand Nachmanides’ interpretation of Moshe’s comments on a slightly deeper level. It is clear that Nachmides interprets Moshe’s main point to be that we should not adopt the rituals of the idolater’s of Canaan because they are meaningless – even ridiculous. As an example, Moshe observes that these idolaters engaged in child sacrifice. Why did Moshe choose specifically this illustration? Certainly, Moshe could have identified other equally bizarre practices. Was this illustration merely arbitrary – perhaps, selected because it is so shocking – or does it imply a specific message?
Nachmanides implies that we are incapable to creating and instituting original rituals. Moshe “proves” his point by referring to child sacrifice. But this is an extreme example. Cannot one respond to Moshe with a counter-argument? It is true that nations of Canaan were sometimes grossly misguided in their concept of worship. Moshe’s illustration does prove this point. But does it follow that therefore, every practice that these nations adopted was depraved?
Apparently, according to Nachmanides, the answer to this second question is that child sacrifice is an extreme example of an overall attitude and misdirection. Any attempt to innovate and invent new rituals is fruitless and dangerous. The inappropriateness of these inventions may not be as evident as in the instance of child sacrifice. Nonetheless, any invention or innovation is inappropriate. Why does Nachmanides insist that we are so woefully incapable of creating new rituals?
In order to understand Nachmanides’ position, let us consider another issue. It has often been observed that although the major religions all regard compassion as a virtue, many of the greatest atrocities in humankind’s history have been performed in the name of religion. Of course, Jews are acutely aware of this phenomenon. Many of the major persecutions that we have experienced – for example, the Crusades – were executed in the name of religion. But this phenomenon is not merely an expression of a hatred for Jews. Throughout history and in modern times it has been common practice for one religious group to persecute and even employ genocide against the members of another religious group. And all of these atrocities are performed in the name of religions that ostensibly hold compassion to be one of the highest virtues.
Let us disregard for this discussion the seeming contradiction in religious doctrine. We will ignore the question of how a religion can preach compassion and at the same time endorse the most shocking forms of violence. Let us focus on the individual. How is it possible for a person to be raised to value compassion and to engage in such atrocities? What happens to this compassionate person? Why does his own personality not rebel against the violence he is contemplating?
There is more than one explanation for this phenomenon. However, let us focus on one factor. The human personality is composed of positive and negative traits. There is a dark side to the human being. Buried in the recesses of the human personality are primitive urges that are kept in check by the positive elements of the personality. Every person has at one time or another been seized by a desire that is unpleasant – even difficult to acknowledge. But hopefully, through the influence of the positive elements of one’s personality, a person is able to hold this objectionable desire in check.
Now, consider the affect of removing the positive elements of the human personality. If these positive elements were removed, then the darkest elements of our personalities would come to the fore. This is exactly what occurs when religion endorses and encourages violence towards others. When a religion condones and incites violence towards others, it incapacitates and suspends the natural barriers that check the dark elements of our personalities. The darkest desires can now emerge and fully express themselves.
Now, let us return to Moshe’s message. The idolaters of Canaan had many forms of worship. How did they develop these rituals? We do not need to engage in an anthropological study to answer this question. In some manner, these rituals were human inventions. They were products of the human imagination and personality. But this is a dangerous source for religious innovation. The human personality is not completely positive. It contains its darker elements – the yetzer hara. In fact, we rely on our religious convictions and training to help check the impulses of the yetzer hara. What happens when rather than religion checking the dark elements of our personality, the influence of the yetzer hara informs our concept of worship? It is likely that the outcome will be a religion that expresses some of the most reprehensible elements of the human personality.
We can now appreciate Moshe’s illustration. Moshe wished to demonstrate that a religion created by human imagination, will undoubtedly reflect the influence of the yetzer hara. In order to illustrate this issue, he could not refer to some ridiculous or meaningless practice. Such and illustration would only prove that we are capable of folly. But Moshe did not want to prove that we are fallible. He wanted to prove that a religion constructed through the human imagination will inevitable, reflect the darker elements of the personality. Moshe illustrated this point with child sacrifice.
Furthermore, according to Nachmanides, Moshe’s contention was that this outcome is unavoidable. The Torah is a revealed religion. It is not a human invention. It is instrumental in checking our darker urges. But when we attempt to invent our own religious innovations, our entire personality is engaged. Nachmanides maintains although we may not suggest human sacrifice, the influences of the yetzer hara cannot be completely removed from our innovations and inventions.
 Rabbaynu Shlomo ben Yitzchak (Rashi), Commentary on Sefer Devarim 12:30.
 Rav Naftali Tzvi Yehuda Berlin (Netziv), Commentary Hamek Davar on Sefer Devarim 12:30.
 Rabbaynu Moshe ben Nachman (Ramban / Nachmanides), Commentary on Sefer Devarim12:30.